I own the Showers Pass jacket. I like it, but one major flaw is that the neck is pretty tight, presumably for keeping rain out. This also makes it hard to layer underneath much in the neck area. Essentially you aren't going to find ONE jacket that is going to be good in 20 degrees as well as 50 degrees. Also walking and riding are very different things in the cold. Cycling generates a lot of heat. Walking doesn't.
I would buy a jacket like the Showers Pass if the neck issue doesn't bother you. Then pick up a nice fleece jacket like a North Face etc. Put a trunk bag on your bike and carry the fleece jacket while riding. When you step off to walk, quickly put on the fleece jacket underneath of your Showers Pass.
Walk briskly and you will be good to go. A trunk bag is invaluable for winter cycling. You can carry clothing adjustments with you and adapt on the go. Before long you will figure out what works with what at what temps and have to adjust less often.
My main advice would be to give up on the notion of finding a jacket that is good for riding and walking unless you are riding very, very slowly.
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